1. Field of the Invention
The present invention relates generally to the field of wireless communications, and in particular, to a device and method for locating the position of a mobile station (MS) in a mobile communication system.
2. Description of the Related Art
The FCC (Federal Communication Commission) of the U.S. provides that an MS locating service should be implemented for emergency 911 (E911) with a probability of 67% within an error of 125 m or below by October of 2001. Therefore, the CDMA (Code Division Multiple Access) standard (TIA/EIA/IS-95) as well as the IMT-2000 (International Mobile Telecommunication-2000) system makes efforts to provide the MS locating service with use of a reverse link function called "PUF (Power Up Function)". The PUF is an MS locating scheme in which an MS in an emergency situation transmits probes with gradually increased power to a plurality of adjacent base stations (BSs) on a reverse channel to inform them of its position so that each of the BSs can calculate the distance between the BS and the MS by estimating the time taken for the signal to reach the BS. The PUF is provided in IS-95B.
Implementation of the PUF, however, increases interference and, as a result, decreases system performance. To overcome the problem, the present invention provides an MS locating method for continuous positioning. The MS locating scheme operates on the principle that an MS receives an active pilot and other neighbor pilots on a forward link channel and estimates its relative position from the neighbor BSs in a CDMA communication system. In addition, relative MS positions from at least three BSs are determined by use of at least two time differences of arrival (TDOAs) of signals received from the BSs. In the present invention, the TDOA and SIR (Signal-to-Interference Ratio) of each BS channel are measured to efficiently determine the position of the MS in a CDMA communication system synchronized to the GPS (Global Positioning System).